| 摘要 |
PURPOSE: To carry out the lighting starting timing control and the dimming control of a hot-cathode discharge tube in a simple constitution by controlling the application of a high-frequency voltage for lighting to the discharge tube by means of a switching element for dimming provided at the secondary winding side of a transformer. CONSTITUTION: When a switching element PhMOS for dimming is provided in parallel to a discharge tube LSL, the high-frequency voltage for lighting of a transformer Tmh is applied as it is to the discharge tube LSL when the PhMOS is OFF so as to light the discharge tube LSL. On the contrary, when the PhMOS is ON, the terminal voltage of the discharge tube LSL is clamped at a value decided by the terminal voltage at the ON condition, and since the value is set less than the lighting voltage, the discharge tube is not lighted. As a result, the discharge tube LSL can be made in the non lighting condition or lighting condition by turning ON and OFF the PhMOS. Consequently, the dimming control and the lighting starting timing control can be carried out with no difficulty by a dimming pulse applied to a transistor Q for driving the switching element PhM0S. |
